The infrared spectrum covers a wide range of wavelengths that are longer than the visible wavelengths, but shorter than the microwave wavelengths. The short-wave infrared (SWIR) wavelengths cover the range of about one to three microns (μm), and certain types of infrared detectors are designed to respond to the energy of wavelengths within the SWIR portion of the infrared region.
An existing material used for manufacturing SWIR focal plane arrays is indium gallium arsenide (InGaAs). State-of-the-art SWIR material is based on bulk and lattice matched InGaAs grown on indium phosphide (InP) substrates, which has a cut-off wavelength of about 1.7 μm at 300K. For applications that require a longer cut-off wavelength in the 2 μm to 3 μm range, and in keeping with the InGaAs material system, a lattice-mismatched (relative to InP) InGaAs alloy with a higher indium composition is needed. This approach, however, degrades performance.
An alternative approach is a strain-layered superlattice using indium gallium arsenide (InGaAs) and gallium arsenide antimonide (GaAsSb) quantum wells. This material system is attractive in that the cut-off wavelength is tunable by extending or shortening the quantum well periods while remaining lattice matched to InP. To extend the spectral cut-off to the 2 μm to 3 μm range, however, the superlattice period must be lengthened dramatically, resulting in weakened coupling of the quantum wells, and a significant drop in the absorption coefficient is observed based on theoretical modeling.
As a result, there is a need for improved techniques for extended strain-layered superlattice materials and methods.